The announcement that a ban would be put in place came just last month following the death of university student Otto Warmbier, who had been sentenced to 15 years in a North Korea prison with hard labor after he tried to steal a banner. At the time of his release, the 22-year-old was in a coma and died several days later.

On Wednesday, Tillerson released a statement saying the travel restriction is “due to the serious and mounting risk of arrest and long-term detention of U.S. citizens under North Korea’s system of law enforcement.”

Journalists and humanitarian workers can apply for an exemption if needed.